1) at baseline at a mean blood pressure (MAP) of 60-65 mmHg (titrated by adjusting the norepinephrine infusion, these patients are generally hypotensive), 2) after increasing norepinephrine infusion to achieve a MAP of 75-80 mmHg, 3) after intravenous infusion of 7,5 ml/kg mL Ringer's acetate (infusion time 10 minutes) during MAP 60-65 mmHg and 4) after MAP has again been adjusted to 75-80 mmHg after the fluid bolus.